1. Field of the Invention
The present invention relates to a pressure sensitive sensor.
2. Description of Background Information
A conventional pressure sensitive sensor, such as the sensor described in Japanese Patent Publication (Kokai) Hei No. 10-281906, is shown in FIG. 8. The conventional pressure sensitive sensor includes a cavity 1a that extends along the inside of a long narrow elastic insulator 1 in a longitudinal direction, and a plurality of electrode wires 3A to 3D are buried in the thickness of the elastic insulator 1 at intervals along the periphery in a circumferential direction. The plurality of electrode wires 3A to 3D are spirally twisted around the cavity 1a, and one section of a peripheral surface of each electrode wire 3A to 3D is exposed in the cavity 1a. Further, when the elastic insulator 1 is elastically deformed, as when the cavity 1a is crushed by pressing, the electrode wires 3A to 3D are brought into conducting contact with each other, therefore external pressure can be detected.
A method of producing the pressure sensitive sensor includes preparing a twisted wire by twisting a spacer, which is of the same shape as the cavity 1a, with a plurality of electrode wires 3A to 3D, and pulling the spacer out after coating the twisted wire with the elastic insulator 1.
However, in the case of the conventional pressure sensitive sensor, complicated production steps of twisting the spacer with the electrode wires 3A to 3D and pulling out the spacer afterward are required to form the structure, and there is a problem of high cost.
Further, the cross-section of the sensor is large in size because of the necessity of forming the cavity 1a in a central location, and the necessity of burying the electrode wires 3A to 3D in the thickness of the elastic insulator 1. For these and other reasons, it is not suitable to make the sensor in a small size.
Further, since there is no procedure for positively separating each of the electrode wires 3A to 3D to insulate them, there is also a danger that when the pressure sensitive sensor is arranged in a warped or kinked section of the insulator, the electrode wires 3A to 3D will be brought in contact with each other by mistake to cause an error in detection.
Accordingly, considering the above-mentioned problems, it is an object of the present invention to provide a pressure sensitive sensor with a simple structure that can be produced easily and at low cost.
Further, another object of the present invention is to provide a pressure sensitive sensor that is appropriate for production with a small cross-sectional area and that can appropriately function even if it is arranged in a warped section with a sharp curvature.
According to an aspect of the present invention, the technical procedure for attaining the above-mentioned objects is to provide a pressure sensitive sensor for detecting pressure by electrical conduction caused by mutual contact by pressing the first and the second electrode members, which are positioned separated from each other, wherein a net braid member that includes an insulating material allows the electrical contact between the first electrode member and the second electrode member through the gap portion of its mesh at the pressure location, and then separates to insulate the first electrode member and the second electrode member when no pressure is provided between the first electrode member and the second electrode member. Preferably, the net braid member is formed by knitting a plurality of yarn materials which are formed of an insulating fiber, and the yarn materials are bundled by coating an insulating resin or rubber on its surface or being impregnated with the insulating resin.
According to a further aspect of the present invention, the first electrode member is an elastic electroconductive tube that includes an elastic electroconductive material, the second electrode member has a long narrow shape that can be bent and extends longitudinally in one direction and a central electrode member which is provided in the elastic electroconductive tube, and the net braid member is provided between the central electrode member and the elastic electroconductive tube so that it covers the outer peripheral surface of the central electrode member.
Further, preferably, the central electrode member has the property that it can recover its shape against a fixed tensile strength and bending deformation, and is provided with a long, narrow central member at least whose outer peripheral portion has elasticity, and an electroconductive metal wire horizontally wound around the outer peripheral portion of the central member in a coil form.
In another aspect of the present invention, the central electrode member is further provided with an electroconductive coating layer including an electroconductive resin or an electroconductive rubber that is provided on the inside of the net braid member so that the outer peripheral surface of the central member is covered outside of the metal wire.
In a further aspect of the present invention, the elastic electroconductive tube is formed by extrusion molding the elastic electroconductive material on the outer peripheral surface of the central electrode member on the outside of the net braid member.
Moreover, preferably, the central electrode member is formed by twisting or bundling a plurality of single metal wires.
Further, the central electrode member may include a single metal wire.
According to an aspect of the present invention, a pressure sensitive sensor for detecting pressure by electrical conduction caused by pressing into contact with each other a first electrode member and a second electrode member provided in a spaced arrangement in an unpressed state is provided including an insulative member provided between the first electrode member and the second electrode member, the insulative member including an insulating material that allows electrical contact between the first electrode member and the second electrode member when pressed and insulates the first electrode member and the second electrode when not pressed. The insulative member may include a net braid member provided between the first electrode member and the second electrode member, the net braid member allowing electrical contact between the first electrode member and the second electrode member through a gap portion in its mesh when pressed, and insulating the first electrode member and the second electrode when not pressed. The net braid member may further be formed by knitting a plurality of yarn strands. The yarn strands may further include an insulating fiber coated on its surface with an insulating resin or rubber, or an insulating fiber impregnated with an insulating resin or rubber.
According to a further aspect of the present invention, the first electrode member may include an elastic electroconductive tube including an elastic electroconductive material, the second electrode member may include a central electrode member having a long narrow bendable shape provided inside the elastic electroconductive tube, and the insulative member may be provided between the central electrode member and the elastic electroconductive tube so that the insulative member covers an outer peripheral surface of the central electrode member. The central electrode member may be restorable to its shape from tensile and bending deformation, and the central electrode member may be provided with a central member having a long narrow shape and having at least an outer elastic peripheral portion and an electroconductive metal wire wound on the outer periphery of the central member in a coil.
In a further aspect of the present invention, the central electrode member may be provided with an electroconductive coating layer including an electroconductive resin or an electroconductive rubber provided on the inside of the insulative member so that an outer peripheral surface of the central member is covered underneath the metal wire. The elastic electroconductive tube may be formed by extrusion molding the elastic electroconductive material on an outer peripheral surface of the central electrode member and covering the insulative member. Further, the central member may be constructed by twisting or bundling a plurality of single metal wires, or may include a single metal wire.
In another aspect of the present invention, the electroconductive metal wire wound on the outer periphery of the central member in a coil may be wound tightly around the central member and embedded into the outer periphery of the central member. The electroconductive metal wire may be embedded in the outer periphery of the central member to substantially half the diameter of the electroconductive metal wire.
According to a further aspect of the present invention, the first electrode member may include a first plate including an elastic electroconductive material, the second electrode member may include a second plate including an elastic electroconductive material, and the insulative member may be provided between the first plate and the second plate. The first and second electrode members may be restorable to their shapes from tensile and bending deformation.
According to another aspect of the present invention a method of making a pressure sensitive sensor for detecting pressure by electrical conduction caused by pressing into contact with each other a first electrode member and a second electrode member provided in a spaced arrangement in an unpressed state is provided including providing an insulative member between the first electrode member and the second electrode member, the insulative member including an insulating material that allows electrical contact between the first electrode member and the second electrode member when pressed and insulates the first electrode member and the second electrode when not pressed. The insulative member may include a net braid member provided between the first electrode member and the second electrode member, the net braid member allowing electrical contact between the first electrode member and the second electrode member through a gap portion in its mesh when pressed, and insulating the first electrode member and the second electrode when not pressed. Further, the net braid member may be formed by knitting a plurality of yarn strands; and the yarn strands may include an insulating fiber coated on its surface with an insulating resin or rubber or the yarn strands may include an insulating fiber impregnated with an insulating resin or rubber.
In a further aspect of the present invention, the method may further include providing a first electrode member including an elastic electroconductive tube including an elastic electroconductive material, providing a second electrode member including a central electrode member having a long narrow bendable shape provided inside the elastic electroconductive tube, and providing the insulative member between the central electrode member and the elastic electroconductive tube so that the insulative member covers an outer peripheral surface of the central electrode member. The method may further include providing the central electrode member with a central member having a long narrow shape and having at least an outer elastic peripheral portion and an electroconductive metal wire wound on the outer periphery of the central member in a coil. Further, the method may include providing the central electrode member with an electroconductive coating layer including an electroconductive rubber provided on the inside of the insulative member so that an outer peripheral surface of the central member is covered underneath the metal wire.
According to a further aspect of the present invention, the method may further include forming the elastic electroconductive tube by extrusion molding the elastic electroconductive material on an outer peripheral surface of the central electrode member and covering the insulative member. The method of making a pressure sensitive sensor may include constructing the central member by twisting or bundling a plurality of single metal wires. Further, winding the electroconductive metal wire on the outer periphery of the central member in a coil may include winding the electroconductive wire tightly around the central member and embedding the electroconductive metal wire into the outer periphery of the central member. Winding the electroconductive metal wire tightly around the central member and embedding the electroconductive metal wire in the outer periphery of the central member may include embedding the electroconductive metal wire to substantially half the diameter of the electroconductive metal wire.
In another aspect of the present invention, the method of making a pressure sensitive sensor may include providing a first electrode member including a first plate including an elastic electroconductive material, providing a second electrode member including a second plate including an elastic electroconductive material, and providing the insulative member between the first plate and the second plate.
In a further aspect of the present invention, a method of using a pressure sensitive sensor for detecting pressure by electrical conduction caused by pressing into contact with each other a first electrode member and a second electrode member provided in a spaced arrangement in an unpressed state is provided including providing a pressure sensitive sensor including a first electrode member, a second electrode member, and an insulative member between the first electrode member and the second electrode member, the insulative member including an insulating material that allows electrical contact between the first electrode member and the second electrode member when pressed, and insulates the first electrode member and the second electrode member when not pressed, and pressing on the pressure sensitive sensor and the insulative member therewith, thus allowing electrical contact between the first electrode member and the second electrode member. The method may further include providing a net braid member between the first electrode member and the second electrode member, the net braid member allowing electrical contact between the first electrode member and the second electrode member through a gap portion in its mesh when pressed, and pressing on the net braid member thus allowing electrical contact between the first electrode member and the second electrode member through the gap portion of the net braid member. In a further aspect of the present invention, a combination is provided including an automobile body, a door, and a pressure sensitive sensor. In a further aspect of the present invention, a combination is provided including an automobile body, a seat, and a pressure sensitive sensor.